A core-less crawler track is provided for comparatively high speed running. A driving system thereof is a structure in which rubber projections are formed from an inner peripheral surface of the crawler with a certain pitch, and a sprocket meshes therewith. The sprocket is generally formed with driving portions, which mesh with the aforementioned rubber projections, and rim portions to left and right of the driving portions, which touch against the inner peripheral surface of the crawler. The driving portions are, for example, a pin type, or a gear type is common. Herein, the present invention will be described with focus on a pin-type sprocket.
FIG. 1 is a sectional view of a sprocket portion of a conventional ordinary crawler-running apparatus, and FIG. 2 is a side view thereof. At a crawler 1, rubber projections 2 with a certain pitch are protrudingly formed at the middle of an inner peripheral surface, and lugs 3 are formed at an outer peripheral surface. Steel cords 4 are embedded, oriented in a length direction of the crawler 1. Further, 5 is a sprocket, at which pins 7 are provided standing at edges of a pair of discs 6, and the sprocket 5 includes rim portions 8 which touch against the inner peripheral surface of the crawler 1 at distal ends of the discs 6. The rubber projections 2 are commonly formed in a substantial isosceles triangle shape with left-right symmetry in side view, as shown in FIG. 3. An angle Z of a base portion of an inclination surface 9 which rises up from the crawler is about 54°.
At the running apparatus of the crawler structured with the crawler 1 and the sprocket 5, in a usual state as shown in the drawings, the rim portions 8 of the sprocket 5 touch against the inner peripheral surface of the crawler 1, and the pins 7 unforcedly mesh with and transmit driving force to a predetermined portion of the inclination surfaces 9 of the rubber projections 2.
However, in the crawler-running apparatus constituted with the structure described above, under high traction, the pins 7 of the sprocket 5 apply large force to the rubber projections 2. Consequently, the rubber projections 2 are greatly deformed, a phenomenon known as jumping (jumping) in which the pins 7 slip arises, and vibrations occur. If this is repeated, there may be a result that the rubber projections 2 are damaged.
Further, as shown in FIG. 4, depositions S of earth, sand and the like at the inner peripheral surface of the crawler 1 may be unavoidable and in such a state, as shown in FIG. 5, a relationship between the rubber projections 2 of the crawler 1 and the pins 7 of the sprocket 5 is shifted from predetermined positions, contacts are repeated, and the rubber projections 2 may be damaged. Ultimately, the aforementioned jumping between the pins 7 and the rubber projections 2 occurs and, further, there may be a result that the rubber projections 2 are damaged.